This invention solved the distortion problem of a circuit board during the rework of a Surface Mounted Technology (SMT) device such as a Ceramic Column Grid Array (CCGA) integrated circuit package, or a Ceramic Ball Grid Array (CBGA) integrated circuit package. The distortion of the circuit board is due high temperature differences during the CCGA rework process. The high temperature differences cause non-uniform expansion of the circuit board. The surface mount attachment specification for CCGA and CBGA states that the reworked area of the circuit board must be flat to 2 mils per inch. Circuit boards with more than 2 mils/inch bow in the reworked site will typically have time zero electrical opens or early reliability fails. The known solution to this problem is to apply a global preheat to the bottom of the circuit board and then use a localized top side heat source to reflow the solder joints of the surface mounted device. The drawback of such known solutions is trying to minimize high temperature differences across the circuit board. An additional solution is required such as this invention because of the large size of the surface mounted device (52.mm CCGA), the long manufacturing cycle time required to heat the circuit board and device, and the temperature differences in the rework site are must be reduced. This invention is also valuable for lead (Pb)-free rework since the Tin/Silver/Copper (SAC) alloy requires a higher temperature for reflow.
U.S. Pat. No. 5,003,160 issued Mar. 26, 1991 to Matsuo et al. for REFLOW FURNACE CONTROL SYSTEM and discloses an improvisation of profile algorithm in the hope of reducing the trial error time required to come up with a desired profile. Specific parameters are generated based on board geometry, component specifics and material used. The furnace sets itself to a preset temperature, speed, etc.
U.S. Pat. No. 5,128,506 issued Jul. 7, 1992 to Dahne et al. for METHOD AND APPARATUS FOR SELECTIVE INFRARED SOLDERING USING SHIELDING FIXTURES discloses selectively soldering components after some components have been attached.
U.S. Pat. No. 5,560,531 issued Oct. 1, 1996 to Ruszowski for REFLOW MINIOVEN FOR ELECTRICAL COMPONENT discloses a single component rework system. The disclosed pick-up system is a spring loaded, vacuum system. A nozzle chimney is used to preheat the part to be reworked.
U.S. Patent Application Publication US2002/0000329 A1 published Jan. 3, 2002 by Hoffmeyer et al. for PROCESSING OF CIRCUIT BOARDS WITH PROTECTIVE ADHESIVE-LESS COVERS ON AREA ARRAY BONDING SITES discloses processing circuit boards containing area array surface treated bonding sites. The circuit board includes a plurality of apertures patterned about the bonding sites for forming a footprint. A protective cover shaped to conform to the footprint includes posts registered to removably fit into the apertures. The protective cover remains overlaid on the circuit board during rework, and then is removed.
U.S. Patent Application Publication US 2005/0071993 A1 published Apr. 7, 2005 by Farooq et al. for BALL GRID ARRAY REWORK USING A CONTINUOUS BELT FURNACE discloses separating interconnects between a card and a substrate. The apparatus includes one or more rotationally biased (spring loaded) partial-circle structures and one or more temperature-sensitive releases connected to the partial-circle structures. The partial-circle structures are positioned to rotate and separate the interconnects when released by the temperature-sensitive releases.
Japanese Patent No. JP2004253406 published Sep. 9, 2004 by Okada Yasuhiro for MODULE COVER AND MEMORY MODULE discloses a module cover and memory module where the memory card has memory chips thereon protected by a cover which, besides being protective, is heat dissipating. This reference appears to address the use of a shield over chips on a printed circuit card.
World Organization Patent WO9623616A1 published Aug. 8, 1996 by David C. Jacks et al. for ATTACHING COMPONENTS AND REWORKING CIRCUIT BOARDS discloses an automatic suction device to remove a chip/module from a locally heated, selectively heated, printed circuit board. A contact heater having hot places prevents adjacent component overheating.